Four members of the Blood Brothers group have denied murdering fellow drug dealer Brendan Vollmost.

A South Windsor man, allegedly murdered by four so-called Blood Brothers, was bashed by the group over a debt before his disappearance, his mother has told a Sydney court.

Giving evidence at the Supreme Court of NSW on Tuesday, Brendan Vollmost's mother Tammy Slade said he told her "they (Blood Brothers) had bashed him and took his jewellery" when she picked him up late one night in a Sydney park.

Jamie Michael Tilley, 36, and Jack Davies, William Patrick Thomas and Mitchell James Bentley, all aged 27, have pleaded not guilty to kidnapping and murdering Mr Vollmost, 23, at South Windsor in March 2015.

The men, who belonged to a group called the Blood Brothers and respectively had the nicknames Coach, Captain, Medium and Smallsie, also deny assaulting Mr Vollmost's friend Ronald Byrnes and a neighbour, Alex Gorman.

Ms Slade told the jury her son dropped off some firewood at her house on March 31 and that was the last time she ever saw him.

The jury has seen CCTV footage from outside Mr Vollmost's home showing him running through a gate towards a back shed, followed by four men, before his body is carried out by two men.

A significant amount of his blood was found in the shed but his body has never been found.

He first mentioned the Blood Brothers around October of the year before, his mother said.

"He got caught up with some guys called the 'Blood Brothers', they were going to be his new family and he would belong," she said.

But soon afterwards he told her he owed them money, she said.

"He wanted money to give to them."

Mr Vollmost rang his mother about 2am one morning asking to be picked up from a park because he had been bashed, she said.

Mr Gorman told the jury he was woken around 11pm that night by screaming and yelling.

Annoyed, he dressed and grabbed a torch to investigate but forgot to pick up his glasses, affecting his vision of objects further than two metres away.

Mr Gorman said he started walking down Mr Vollmost's driveway shining his torch and saw "several people".

A man ran up to him and said "'oi you silly prick, you should have stayed in the house'" before punching him in the face.